How do I fix render-blocking JavaScript?

Do not let third-party tags run as synchronous parser-blocking scripts. Add async or defer, load them after first paint, or proxy them through a tag manager that does. PicPerf Turbulence adds async to known-safe third-party scripts such as GTM and common analytics snippets.

Will that fix Total Blocking Time?

It helps when TBT is caused by those third-party tags. It will not shrink your own application bundle. Measure the waterfall before you assume the tag manager is the whole problem.

How to fix render-blocking JavaScript

Parser-blocking third-party scripts delay first paint and inflate total blocking time. Load known-safe tags asynchronously, or let PicPerf Turbulence do it.

Last updated: August 15, 2026

Render-blocking JavaScript is a script the browser must download and run before it can paint. On marketing sites it is often Google Tag Manager, analytics, or a chat widget in the <head> without async. That shows up as high total blocking time and weaker INP.

What to change

Identify parser-blocking third-party scripts in the waterfall.
Give them async or load them after first paint.
Do not “fix” your own critical bundle by only flipping async — you can break hydration.

What PicPerf Turbulence changes

Known-safe third-party scripts (GTM, common analytics, similar tags) get async so they stop blocking HTML parse. That is one reason the ~500-site lab set showed about 25% less total blocking time. Turbulence does not rewrite your application JavaScript or delay every script on the page.

Pair this with LCP work and a monitor from the performance stack.

Frequently asked questions

Do not let third-party tags run as synchronous parser-blocking scripts. Add async or defer, load them after first paint, or proxy them through a tag manager that does. PicPerf Turbulence adds async to known-safe third-party scripts such as GTM and common analytics snippets.
It helps when TBT is caused by those third-party tags. It will not shrink your own application bundle. Measure the waterfall before you assume the tag manager is the whole problem.

Related guides

What is PicPerf Turbulence? A definition of PicPerf Turbulence as an edge HTML optimizer, not just an image CDN.
Improve Core Web Vitals without changing code How to raise LCP, INP, and CLS with a DNS change instead of a refactor.
How to fix Largest Contentful Paint What usually delays LCP and how PicPerf Turbulence addresses image and font weight.
Best frontend performance tools The stack that makes a site faster, finds why it is slow, and measures real users.

PicPerf Turbulence rewrites every HTML page at the edge. No code changes.

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